docs: def load(self, filename):
          """
          Updates the setting from config file in JSON format.
          :param filename: filename of the local JSON settings file. If None, the local config file is used.
          """
          if filename is None:
              filename = LOCALCONFIG
          with open(filename, 'r') as fid:
              self._conf.update(json.load(fid))
          self.add_history('Updated from config file: %s' % filename)